After some quick google searching, I can't find any evidence supporting #1. (So in the mean time while we figure this out, you should probably still wear helmets while cycling, folks).
This article makes an important point: studies prove people in accidents have significantly reduced head damage. However, not many studies prove that it makes bicycling safer: instead, cyclers are perceived safer, and therefore it is unsafer.
This article makes an important point: studies prove people in accidents have significantly reduced head damage. However, not many studies prove that it makes bicycling safer: instead, cyclers are perceived safer, and therefore it is unsafer.